1991 LEXUS SC400 brake

15
ABBREVIATIONS
DISCONNECTION AND CONNECTION OF BOLT
TYPE CONNECTORS
For engine and ECT ECU in this vehicle, connectors are used
which require a bolt built into the connector to be screwed down to
securely connect the connector.
1. Disconnect the connectorAfter completely loosening the bolt, the two parts of the
connector can be separated.
NOTICE:
Do not pull the wire harness when disconnecting the
connector.
2. Connect the connector
NOTICE:
Before connecting the connector, always check that the
terminals are not bent or damaged.
(a) Match the guide section of the male connectorcorrectly with the female connector, then press them
together.
(b) Tighten the bolt. Make sure the connectors are completely connected,
by tightening the bolt until there is a clearance of less
than 1 mm (0.04 in.) between the bottom of male
connector and the end of female connector.
ABBREVIATIONS
The following abbreviations are used in this manual.
A/C = Air Conditioning O/D = Overdrive
ABS = Anti±Lock Brake System R/B = Relay Block
A/T = Automatic Transmission RH = Right±Hand
CB = Circuit Breaker SRS = Supplement Restraint System
COMB. = Combination SW = Switch
ECT = Electronic Controlled Transmission TDCL = Total Diagnostic Communication Link
ECU = Electronic Control Unit TEMP. = Temperature
EGR = Exhaust Gas Recirculation TRAC = Traction Control
FL = Fusible Link VSV = Vacuum Switching Valve
ISC = Idle Speed Control W/ = With
J/B = Junction Block W/O = Without
LH = Left-Hand
* The titles given inside the components are the names of the terminals (ter\
minal codes) and are not treatedas being abbreviations.
WhereEverybodyKnowsYourName

143
ABS (ANTI±LOCK BRAKE SYSTEM)
WhereEverybodyKnowsYourName

144
ABS (ANTI±LOCK BRAKE SYSTEM)
M
A
11
MR A
4
R± A
5
SR
A
6 SFL
A
12 SRR
A
8 AST
A
9 MT
B
1 SFR
B
16 PKB
B
2 GND
B
13 GND
B
1B 4 B
3B 2B5
A 4
A 3
A 1 2 1
IG1
19
IO1
5IO1 7
EB EA 16 22 23 11
EB1
6IK1 10
IJ
EA 1
34
3 2
16
1
4
2
IK2
25 IK2 2
IE1
1
IE2
12
2 1
E10
I23I25
E9
2
6 6
666
66
66
6
B
10
WA
B
6
TS
5
6
E12 L
P±B
V±Y
L±W
L±W L
W
V±YL
W± B L±W V±YY±L
R
R
R
B±R
B±R
B±R
P±B
V
L
L
L V
L V±Y
V
R±Y
Y
B±Y P
L±W Y±G
R±W R±W
W±B
W±B
R±W
R±W
B
B
W±B
W±B W±B
W±B W±B
L±WL
W± B
SFR SFL SRR AST MT
BS
BM
GND WA
TS TC
WB
BATTERY ABS ECU
(
W/O TRACTION CONTROL )
R
120A ALT
60A ABS NO. 1
ABS MOTOR
RELAY
ABS ACTUATOR
RELAY
CHECK
CONNECTOR
FUSE BLOCK
R±W
DIODE
(FOR PARKING BRAKE )
BRAKE FLUID
LEVEL SW
PARKING
BRAKE
SW
ABS ACTUATOR
(
CANA DA )
( USA )
B1
D2
A4 , A33
P3
A2 2
,A23
B
BA A
C3
F9 SHORT PIN
WhereEverybodyKnowsYourName

146
ABS (ANTI±LOCK BRAKE SYSTEM)
THIS SYSTEM CONTROLS THE RESPECTIVE BRAKE FLUID PRESSURES ACTING ON THE DISC\
BRAKE CYLINDERS OF THE RIGHT
FRONT WHEEL, LEFT FRONT WHEEL AND REAR WHEELS WHEN THE BRAKES ARE APPLIED IN \
A PANIC STOP SO THAT THE
WHEELS DO NOT LOCK. THIS RESULTS IN IMPROVED DIRECTIONAL STABILITY AND STEERABILITY DURING PANIC BRAKING.
1. INPUT SIGNALS
(1) SPEED SENSOR SIGNALTHE SPEED OF THE WHEELS IS DETECTED AND INPUT TO TERMINALS FL+, FR+, RL+ AND RR+ OF THE ABS ECU.
(2) STOP LIGHT SW SIGNAL A SIGNAL IS INPUT TO TERMINAL STP OF THE ABS ECU WHEN THE BRAKE PEDAL IS OPERATED.
(3) PARKING BRAKE SW SIGNAL A SIGNAL IS INPUT TO TERMINAL PKB OF THE ABS ECU WHEN THE PARKING BRAKE IS OPERATED.
2. SYSTEM OPERATION
DURING SUDDEN BRAKING, THE ABS ECU WHICH HAS SIGNALS INPUT FROM EACH SENSOR CONTROLS THE CURRENT FLOWING
TO THE SOLENOID INSIDE THE ACTUATOR AND LETS THE HYDRAULIC PRESSURE ACTING ON EACH WHEEL CYLINDER ESCAPE \
TO
THE RESERVOIR.
THE PUMP INSIDE THE ACTUATOR IS ALSO OPERATING AT THIS TIME AND IT RETURNS THE BRAKE FLUID FROM THE RESERVOIR
TO THE MASTER CYLINDER, THUS PREVENTING LOCKING OF THE VEHICLE WHEELS.
IF THE ECU JUDGES THAT THE HYDRAULIC PRESSURE ACTING ON THE WHEEL CYLINDER IS INSUFFICIENT, THE CURRENT
ACTING ON SOLENOID IS CONTROLLED AND THE HYDRAULIC PRESSURE IS INCREASED.
HOLDING OF THE HYDRAULIC PRESSURE IS ALSO CONTROLLED BY THE COMPUTER, BY THE SAME METHOD AS ABOVE. BY
REPEATED PRESSURE REDUCTION, HOLDING AND INCREASE ARE REPEATED TO MAINTAIN VEHICLE STABILITY AND TO IMPROVE
STEERABILITY DURING SUDDEN BRAKING.
A 4(B), A 33(A) ABS ACTUATOR
(A) 3, (A) 4±GROUND : ALWAYS APPROX. 12 VOLTS
(A) 1±GROUND : ALWAYS CONTINUITY
(B) 4, (B) 5, (B) 6±GROUND : APPROX. 1.15
(IGNITION SW OFF)
(B) 2±GROUND :APPROX. 5
(IGNITION SW OFF)
A 7, A 8, A30, A31 ABS SPEED SENSOR FRONT LH, RH, REAR LH, RH
1±2 : APPROX. 1.0KW (20 °C, 68°F)
A22(A), A23(B) ABS ECU
(B) 11±GROUND : APPROX. 12 VOLTS WITH IGNITION SW ON
(B) 2, (B) 13±GROUND : ALWAYS CONTINUITY
(B) 22±GROUND : ALWAYS APPROX. 12 VOLTS
(B) 1, (A) 6, (A) 12±GROUND : APPROX. 12 VOLTS WITH IGNITION SW ON
(B) 16±GROUND : CONTINUITY WITH PARKING BRAKE LEVER PULLED UP
(B) 7±GROUND : APPROX. 12 VOLTS WITH STOP LIGHT SW ON
P 3 PARKING BRAKE SW
1±GROUND : CLOSED WITH PARKING BRAKE LEVER PULLED UP
S12 STOP LIGHT SW
1±2 : CLOSED WITH BRAKE PEDAL DEPRESSED
SYSTEM OUTLINE
SERVICE HINTS
WhereEverybodyKnowsYourName

135
B
4 RL+
B
15 RL±
B
5 RSS
B
14 RR+
B
3 ALT
BW1
3BW1 8
BW1
2
BW1
5
BW1
6
Bc2
6
Bc2
2 I26
12 12
W O W±B
L±G
L±Y
W
O
L±G L±Y
W
O
L±G L±Y
(
SHIELDED ) (
SHIELDED )
(
SHIELDED )
REAR LH REAR RH A3 1
A3 0
ABS SPEED SENSOR
M
6
1
4
36
6
66
TRACTION BRAKE
MAIN RELAY
2 16 22
3
1 23 11
E7
I25 I32
I23
EB1
6
IO1
7 IK2
2
A
23
MTT A
1
TSR A
20
E2 A
19
VC A
10
PR A
15
SRC A
2
SMC A
12
SAC C
1
TS B
9
WA C
3
TC
A
1A 2A3
A
4A 5A6
B
2
B
1 B
4
L±Y
B±R
L
L
L
L VB±R
P±B
P±B B±R
R±W
R±W
R±W
W
R
B
V±Y V
V±W B±R
R
R±W
V±Y
TS WA
R
B±R
L±Y
W±B V±Y
W±B W±B P±B
L
TC
WB
T5 T3
,
T4C3
TRACTION PUMP
AND MOTOR TRACTI ON BRA KE
ACTUATOR
CHECK
CONNECTOR
BA
(
SHIELDED )
C
ABS AND TRACTION ECU A24 ,
A25 ,A26
AB P±B
P±B
ACC CUT MIC CUT
RESERVOIR
CUT
(
SHIELDED )
A
17 FR+
A
4 FR±
A
16 FS S
I26
21(
SHIELDED )
O±L
W±L W±B
W±L O±L
A8
FRONT RH B
8
IO1
10
3B
1
3B
2
IJ 1
5 IG3
1
A1 0
ALTERNATOR Y±G
Y±G
Y±G
Y±G
Y±G
RR±
I26
B17
BR
BR
I26
B34
BW1
7
Bc2
5 B17
B36
BR±B BR±B BR±B
BR±B
(
SHIELDED )
2
SHORT
PIN
WhereEverybodyKnowsYourName

136
ABS AND TRACTION CONTROL
I16E9
I14
I25 I25
I4
E13 I7
1E
12 1I 10 2 1I 8
14 8 17 4
IO1
8
IK2
9 3E
3
A1
B
15 B 5B1
B
22 GND1
B
2 GND2
B
13 GND3
B
6 LBL
B
17 PKB C
7 ABSO
C
12 BRP
C
8 BRC
C
7 THFA
C
11 BRFA
C
15 FRO
C
6 FL O
C
10 P
C
5 N
B
20
D/G B
10
STP B
21
BATT A
24
IG
3A
4
3D13
IK25 IO1
1IE2 7
1 2
I7 1H1
1E20
FROM POWER SOURCE SYSTEM
(
SEE PAGE 56 )
2 1 2 1
2 1 1
EA
IJ IG1
19 IG1 20IK2
18
IE2
12 IE1
1 IO1
9
P±B
Y
W
G±W
G±W
R
B±R
B±R R
G±W
Y
LG±R W
L V±W
L±Y W
G±W B±R
R±B
R±B
L
GR LG
LG±B P±L
P±G
V±R
B±Y
W±B
W±B
W±B
R±W
R±W
R±W
R±W
B
R±W
R±W
R±WR±B
B
W±B W±B W±B
V±W
L±Y
L
P±B
R±W R±W
B WW
R±W
10A
GAUGE
15A
STOP10A
DOME15A
ECU±IG
WTRC
ABS TC
G±W
COMBINATION METER STOP LIGHT
SW
TDCL
ABS AND TRACTION ECU
B
B
PARKING
BRAKE SW
BRAKE FLUID
LEVEL SW
DIODE
(FOR BRAKE FLUID LEVEL )
DIODE
( FOR P ARK I NG
BRAKE ) (
CANADA )
(
USA )
A24
,A2 5
,A26
C13
,
C14
T6 S12
P3
B1 D1
D2
B
A
B B±R
R
G± W
LG±R W
L±Y
B±Y
V±R
P±G P±L
LG±B LG
GR L
R±B
R±W
IK 1
10
3H
12
P±B
TRAC OFF TRAC ANTI
LOCK
A
B 2
1
P±B
P±B
P±B
WhereEverybodyKnowsYourName

139
(FOR ABS)
THIS SYSTEM CONTROLS THE RESPECTIVE BRAKE FLUID PRESSURES ACTING ON THE DISC\
BRAKE CYLINDERS OF THE RIGHT
FRONT WHEEL, LEFT FRONT WHEEL AND REAR WHEELS WHEN THE BRAKES ARE APPLIED IN \
A PANIC STOP SO THAT THE
WHEELS DO NOT LOCK. THIS RESULTS IN IMPROVED DIRECTIONALLY STABILITY AND STEERABILITY DURING PANIC BRAKING.
1. INPUT SIGNALS
(1) SPEED SENSOR SIGNALTHE SPEED OF THE WHEELS IS DETECTED AND INPUT TO TERMINALS FL+, FR+, RL+ AND RR+ OF THE ABS AND TRACTION
ECU.
(2) STOP LIGHT SW SIGNAL A SIGNAL IS INPUT TO TERMINAL STP OF THE ABS AND TRACTION ECU WHEN THE BRAKE PEDAL IS OPERATED.
(3) PARKING BRAKE SW SIGNAL A SIGNAL IS INPUT TO TERMINAL PKB OF THE ABS AND TRACTION ECU WHEN THE PARKING BRAKE IS OPERATED.
2. SYSTEM OPERATION
DURING SUDDEN BRAKING, THE ABS AND TRACTION ECU WHICH HAS SIGNALS INPUT FROM E\
ACH SENSOR CONTROLS THE
CURRENT FLOWING TO THE SOLENOID INSIDE THE ACTUATOR AND LETS THE HYDRAULIC PRESSURE ACTING ON EACH WHEEL
CYLINDER ESCAPE TO THE RESERVOIR. THE PUMP INSIDE THE ACTUATOR IS ALSO OPERATING AT THIS TIME AND IT RETURNS
THE BRAKE FLUID FROM THE RESERVOIR TO THE MASTER CYLINDER, THUS PREVENTING LOCKING OF THE VEHICLE WHEELS.
IF THE ECU JUDGES THAT THE HYDRAULIC PRESSURE ACTING ON THE WHEEL CYLINDER IS INSUFFICIENT, THE CURRENT
ACTING ON SOLENOID IS CONTROLLED AND THE HYDRAULIC PRESSURE IS INCREASED, HOLD\
ING OF THE HYDRAULIC
PRESSURE IS ALSO CONTROLLED BY THE COMPUTER, BY THE SAME METHOD AS ABOVE. BY REP\
EATED PRESSURE REDUCTION,
HOLDING AND INCREASE ARE REPEATED TO MAINTAIN VEHICLE STABILITY AND TO IMPROVE STEERABILITY DURING SUDDEN
BRAKING.
(FOR TRACTION CONTROL)
THE TRACTION CONTROL SYSTEM IS A SYSTEM WHEREBY THE ªABS AND TRACTION ECUº AND ªTRACTION ECUº\
CONTROLS THE
ENGINE TORQUE AND THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER OF THE DRIVING WHEELS IN ORDER TO CONTROL
SPINNING OF THE DRIVING WHEELS WHEN STARTING OFF AND ACCELERATING, AND PROVIDE THE MOST APPROPRIATE DRIVING
FORCE IN RESPONSE TO THE ROAD CONDITIONS FOR VEHICLE STABILITY.
TRACTION CONTROL OPERATION
VEHICLE SPEED SIGNALS FROM THE SPEED SENSOR INSTALLED ON EACH WHEEL ARE INPUT TO THE ABS AND TRACTION ECU.
WHEN THE ACCELERATOR PEDAL IS DEPRESSED WHILE DRIVING ON A SLIPPERY ROAD AND THE DRIVING WHEEL (REAR WHEEL)
SLIPS, IF THE ROTATION OF THE REAR WHEEL EXCEEDS THE ROTATION OF THE FRONT WHEELS FOR A SPECIFIED PERIOD, THE
ECU JUDGES THAT THE REAR WHEEL IS SLIPPING.
WHEN THIS OCCURS, CURRENT FLOWS FROM TRACTION ECU TO SUB THROTTLE ACTUATOR TO CLOSE THE SUB THROTTLE
VALVE. THE THROTTLE VALVE OPENING ANGLE SIGNAL IS OUTPUT FROM TERMINAL VTA OF SUB THROTTLE POSITION SENSOR
TO TERMINAL VTA2 OF ENGINE AND ECT ECU TO KEEP THE ENGINE RPM AT THE MOST SUITABLE LEVEL FOR THE DRIVING
CONDITIONS AND REDUCE SLIP OF THE DRIVING WHEEL. AT THE SAME TIME, OPERATION OF THE ABS AND TRACTION ECU
CAUSE THE TRACTION BRAKE ACTUATORS (ACC CUT, M/C CUT, RESERVOIR CUT SOLENOID) TO TURN ON TO SWITCH THE
HYDRAULIC CIRCUIT TO ªTRACTIONº MODE.
IN THIS CASE, SIGNALS ARE INPUT FROM TERMINAL SRR OF ABS AND TRACTION ECU TO TERMINAL (B)6 OF ABS ACTUATOR, AND
FROM TERMINAL SRL OF ABS AND TRACTION ECU TO TERMINAL (B)1 OF ABS ACTUATOR, CONTROLLING THE REAR WHEEL
SOLENOID IN THE ABS ACTUATOR AND INCREASING THE HYDRAULIC PRESSURE OF THE WHEEL CYLINDER IN ORDER \
TO
PREVENT SLIP.
TO MAINTAIN THE HYDRAULIC PRESSURE OF THE REAR WHEELS, THE REAR WHEEL SOLENOID I\
NSIDE THE ABS ACTUATOR IS
PUT IN ªHOLDº MODE AND KEEPS THE HYDRAULIC PRESSURE TO THE BRAKE CYLINDER CONSTANT.
WHEN THE BRAKE CYLINDER HYDRAULIC PRESSURE IS REDUCED, THE PRESSURE REDU\
CTION MODE REDUCES AND CONTROLS
THE HYDRAULIC PRESSURE.
SYSTEM OUTLINE
WhereEverybodyKnowsYourName

140
ABS AND TRACTION CONTROL
A24(A), A25(B), A26(C) ABS AND TRACTION ECU
(B) 21±GROUND : ALWAYS APPROX. 12 VOLTS
(B) 11±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
(B) 10±GROUND : CONTINUITY WITH STOP LIGHT SW ON
(B) 2, (B) 13, (B) 22±GROUND : ALWAYS CONTINUITY
(B) 17±GROUND : CONTINUITY WITH PARKING BRAKE LEVER PULLED UP (PARKING BRAKE SW ON)
A 4(B), A 5(C), A 6(A) ABS ACTUATOR
(A) 1, (A) 2±GROUND : APPROX. APPROX. 12 VOLTS
(C) 1±GROUND : ALWAYS CONTINUITY
(B) 1, (B) 5, (B) 4, (B) 6±GROUND : APPROX. 1.15 (IGNITION SW OFF)
(B) 2±GROUND : APPROX. 5 (IGNITION SW OFF)
T3(A), T 4(B) TRACTION BRAKE ACTUATOR
(B) 2± (B) 4 : OPEN ABOVE APPROX. 134.5KG/CM2
(13189 KPA, 1910PSI)
CLOSED BELOW APPROX. 95KG/CM2 (9316 KPA, 1349PSI)
(A) 3± (A) 6 : APPROX. 2
(A) 2± (A) 5 : APPROX. 2
(A) 1± (A) 4 : APPROX. 2
S12 STOP LIGHT SW
2±1 : CLOSED WITH BRAKE PEDAL DEPRESSED
A 7, A 8, A30, A31 ABS SPEED SENSOR FRONT LH, RH, REAR LH, RH
1±2 : APPROX. 1.0(20 °C, 68°F)
T13(B), T14(A) TRACTION ECU
(A) 2±GROUND : APPROX. 12 VOLTS WITH IGNITION SW AT ON POSITION
(A) 15±GROUND : ALWAYS APPROX. 12 VOLTS
(A) 20, (A)14±GROUND : ALWAYS CONTINUITY
(A) 1±GROUND : CONTINUITY WITH PARKING BRAKE LEVER PULLED UP
(B) 2±GROUND : APPROX. 12 VOLTS WITH STOP LIGHT SW ON
(B) 13±GROUND : CONTINUITY WITH TRACTION CUT SW PUSHED ON
(B) 8±GROUND : ALWAYS APPROX. 12 VOLTS
P 3 PARKING BRAKE SW
1±GROUND : CLOSED WITH PARKING BRAKE LEVER PULLED UP
S 8 SUB THROTTLE ACTUATOR
2±1, 2±3 : APPROX. 0.9
5±4, 5±6 : APPROX. 0.9
: PARTS LOCATION
CODESEE PAGECODESEE PAGECODESEE PAGE
A 4B26C 326S 927
A 5C26C13B28S1229
A 6A26C14A28T 227
A 726D 128T 3A27
A 826D 228T 4B27
A1026E 226T 527
A24A28E 326T 629
A25B28E 9A28T1229
A26C28E10B28T13B29
A3030F 926T14A29
A3130P 329
B 126S 827
: RELAY BLOCKS
CODESEE PAGERELAY BLOCKS (RELAY BLOCK LOCATION)
219ENGINE COMPARTMENT LEFT624ENGINE COMPARTMENT LEFT
SERVICE HINTS
WhereEverybodyKnowsYourName